Integrated air cycle-gas turbine engine

ABSTRACT

An additional turbine, an air-to-water heat exchanger, and an air-to-air heat exchanger are added upstream of a recuperated gas turbine engine. Incoming air at atmospheric temperature is expanded and cooled in the additional turbine and then passes through the air-to-water heat exchanger where it is used to cool warm water to a suitable drinking temperature. The cool air then passes through the air-to-air heat exchanger, where it precools the incoming atmospheric temperature air. The output shaft of the additional turbine is coupled to an additional compressor downstream of the original compressor of the engine, thus resulting in a higher net pressure ratio.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a divisional of U.S. Pat. application Ser. No. 804,048, filedDec. 9, 1991, now U.S. Pat. No. 5,212,942 which was a divisional of U.S.Pat. application Ser. No. 611,418, which was filed Nov. 9, 1990, and isnow U.S. Pat. No. 5,105,617.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates in general to turbine engines.

More particularly, the invention relates to a turbine engine having animproved recuperator which utilizes the high temperature gases exhaustedfrom the turbine to preheat compressed air from the compressor prior toits entry into the combustor.

In a further and more specific aspect, the invention relates to arecuperated gas turbine engine integrated with an air-conditioning orcooling cycle.

2. Prior Art

A simple gas turbine engine or power plant comprises a combustionchamber having inlets for receiving compressed air and fuel, acompressor for compressing the air prior to its entry into thecombustion chamber, and a turbine for extracting energy from the hotgases exhausted from the combustor. A portion of the energy extracted bythe turbine is used to rotate a drive shaft coupled to the compressor.

Numerous techniques are known for increasing the thermal efficiency, andthereby decreasing the net fuel consumption, of such an engine. Onecommon technique is to direct the hot exhaust gases from the turbinethrough a heat exchanger, known as a recuperator, which heats thecomparatively cold air from the compressor prior to its entry into thecombustor. As a result, less fuel is required in the combustor forproducing a given turbine inlet temperature.

Prior art recuperators have taken a multitude of differentconfigurations. One common type of recuperator is the tubular type,which comprises a plurality of parallel tubes oriented parallel to theengine centerline in an annular matrix with an inlet manifold at one endand an outlet manifold at the other end. Another common type ofrecuperator comprises a plurality of plates of relatively thin material,so formed and stacked as to provide heat transfer through the plates toand from a series of alternate flow passages formed between the stacked,alternate plates.

Both the tubular type and the stacked plate type of recuperators sufferfrom a number of shortcomings which reduce their overall thermalefficiency and/or make them impractical for many applications. Forinstance, the tubular type recuperators utilize a large amount ofexternal ducting, and require a large amount of space in an engine.Thus, they are unsuitable for use in environments such as automotive andjet engines, where compact size and minimal weight are essential.Stacked-plate type recuperators require a large amount of welding andbrazing, which means that all the components must be constructed ofcompatible materials. Thus, even those components which only come intocontact with the relatively low temperature (approximately 350° F.) airfrom the compressor must be constructed from the same high grade alloysas those components which come into contact with the high temperature(approximately 1400° F.) turbine exhaust. This adds unnecessarily to thecost of manufacturing the engine.

Another problem confronting the designers of prior art recuperators hasbeen the high amount of thermal stress due to the large temperaturegradients in the different components of the recuperator, and thethermal expansions and distortions which result. Still another problemhas been the lack of adequate sealing between adjacent flow passages ofthe recuperation resulting in leakage of the high pressure air from thecompressor into the low pressure side of the recuperator Thus theoverall pressure ratio, and as a result, the efficiency, of the systemis reduced.

Another shortcoming of prior art recuperated engines has been that therecuperator usually encompasses only a small part of the engine. Thus,only a fraction of the waste heat generated by the turbine and combustoractually passes through the heat exchanger. The rest of the heat is lostthrough radiation.

Another factor affecting the efficiency of gas turbine recuperators isthe amount of turbulence within the fluid flow passages It is generallywell known that heat transfer is most efficient when the flow is in theturbulent regime. Commonly, turbulence is induced by inserting strips orrods of twisted metal, known as turbulators, into the flow passages of arecuperator. However, this has only been possible with flow passages ofrelatively simple construction, such as in straight tube-typerecuperators. Other types of recuperators having convoluted or verysmall-diameter flow passages have not been suitable for the inclusion ofturbulators.

In addition to recuperation, other techniques are known for increasingthe net efficiency of a gas turbine engine. One technique iscogeneration, in which the waste heat from the energy. A problem withmost cogeneration systems, however, is that the energy output variesaccording to the load. Therefore, as the load decreases, the temperatureof the turbine exhaust decreases as well. This is undesirable, sincemost boilers are designed for constant heat input.

Other ways of increasing the efficiency of an engine includeintercooling and reheating. In intercooling, the incoming air iscompressed in stages before entering the combustor. Between stages, theair passes through a heat exchanger, known as an intercooler, where thetemperature of the air is lowered. In reheating a second combustor isadded for raising the temperature of the gases to a maximum level. Bothof these techniques increase the energy output of the engine, since theenergy output is proportional to the difference between the lowest andhighest temperatures in the system. However, even in these types ofsystems, a certain amount of energy is wasted, since no attempts havebeen made to utilize the heat drawn from the compressed air in theintercooler.

It would be highly advantageous, therefore, to remedy the foregoing andother deficiencies inherent in the prior art.

Accordingly, it is an object of the present invention to improve thethermal efficiency of a turbine engine.

Another object of the invention is to provide a gas turbine engine witha primary surface counterflow recuperative heat exchanger.

And another object of the invention is the provision of a recuperativeheat exchanger which entirely surrounds the components of a gas turbineengine.

Still another object of the invention is to provide a recuperative heatexchanger with an improved configuration in which all waste heat isradiated from the hottest point in the engine to the coolest point, toensure maximum thermal efficiency.

Yet another object of the invention is the provision of a gas turbinerecuperator requiring minimal brazing and welding so that multiplealloys can be used.

And yet another object of the invention is to provide a gas turbinerecuperator which eliminates the problem of leakage between high and lowpressure flow passages.

Yet still another object of the invention is the provision of a gasturbine recuperator which is suitable for the inclusion of turbulators.

And a further object of the instant invention is to minimize the amountof external ducting in a recuperated gas turbine engine.

And yet a further object of the invention is to provide a recuperatedgas turbine engine which can be integrated with an air-conditioning orcooling cycle.

And still a further object of the invention is the provision of alow-cost, lightweight Integrated air cycle-gas turbine engine accordingto the foregoing which is suitable for military applications.

SUMMARY OF THE INVENTION

Briefly, to achieve the desired objects of the instant invention inaccordance with the preferred embodiments thereof, a gas turbine engineis provided with an improved recuperator for increasing the thermalefficiency of the system.

More specifically, the recuperator is a primary surface counterflow heatexchanges in the form of three concentric cylindrical shells whichcompletely encircle the hottest components of the engine, including theturbine nozzle and the combustion chamber. The outermost shell includesa plurality of longitudinally spaced apart inlet openings which openinto a header receiving relatively low temperature air from thecompressor, and a plurality of longitudinally spaced apart outletopenings, diametrically opposite the inlet openings, which communicatewith a connector duct leading to the combustion chamber. The innermostshell includes a plurality of inlet openings which receiving hightemperature gases discharged from the turbine, and a plurality of outletopenings, diametrically opposite the inlet openings, which communicatewith an exhaust duct leading out of the engine. The central shell is acorrugated tube which acts as a separator wall preventing mixing of thehigh pressure air discharged from the compressor with the low pressuregases discharged from the turbine, but allowing heat transfertherebetween. The spaces between each corrugation, or fold, of thecentral shell and the outer shell define a plurality of annular flowchambers for the high pressure, relatively low temperature air, whilethe corresponding spaces between the central shell and the inner shelldefine a plurality of annular flow chambers for the low pressure,relatively high temperature turbine exhaust gases.

The outer shell of the recuperator is preferably resistance-welded tothe casing of the engine at each of its ends, and the opposite ends ofthe central shell are resistance welded to the outer shell at the samelocation. The inner shell, which is normally spaced from the folds ofthe central shell to allow for thermal expansion in a radial direction,is held in place at one end by a radially out-turned flange which isloosely clamped between the Central shell of the recuperator and an endwall of the casing. The opposite end of the inner shell is unrestrained,to allow for thermal expansion in a longitudinal direction. Because nobrazing is required to hold the inner shell in place, compatibility ofmaterials is not a consideration Thus, the inner shell, which is exposedto the extremely high temperature exhaust from the turbine, can beconstructed from a relatively high grade alloy, while the central andouter shells, which are exposed to the lower temperature from thecompressor, can be constructed from less expensive, lower grade alloys

Specially configured turbulators are provided for inclusion between thecorrugations of the central shell. Each turbulator is formed by punchinga plurality of holes of a desired configuration into a thin, rectangularsheet of a malleable metal, and crimping one longitudinal edge of thesheet by passing it through a pair of meshing, dentate rollers. Theshorter length of the crimped edge relative to the uncrimped edge causesthe sheet to curve about an axis perpendicular to a line parallel to thecrimped edge, until the lateral edges of the sheet nearly contact oneanother, and the sheet forms a slightly wavy ring. The pattern of wavesand holes on the surface of each turbulator ring forces the fluid in therecuperator to take a tortuous path through the annular flow chambers,thus inducing turbulence for more efficient heat transfer.

In one embodiment of the invention, a gas turbine engine provided withthe improved recuperator is part of a cogeneration system in which thewaste heat from the turbine is exhausted into an energy recovery devicesuch as a boiler for producing steam heat. A temperature-controlledvalve is provided at the turbine outlet for regulating the proportion ofwaste heat passing through the recuperator relative to the amount ofwaste heat exhausting directly into the boiler, thus ensuring that thetemperature of gases entering the boiler is constant.

In another embodiment of the invention, the recuperated gas turbineengine is incorporated into a cogeneration system using intercooling andreheating. More specifically, the inlet air is compressed in stages, andan air-to-water heat exchanger is interposed between the two stages.Warm water exiting the air-to-water heat exchanger can be delivered tothe boiler downstream of the turbine exhaust, or it can be diverted toan alternative warm water output device such as a faucet.

In still another embodiment of the invention, the recuperated gasturbine engine may be integrated with an air cycle using a techniqueknown as "boot strapping", in which an additional turbine, anair-to-water heat exchanger, and an air-to-air heat exchanger are addedupstream of the engine. Incoming air at atmospheric temperature isexpanded and cooled in the additional turbine and then passes throughthe air-to-water heat exchanger where it is used to cool warm water to asuitable drinking temperature. The cool air then passes through theair-to-air heat exchanger, where it precools the incoming atmospherictemperature air. The output shaft of the additional turbine is coupledto an additional compressor downstream of the original compressor of theengine, thus resulting in a higher net pressure ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and further and more specific objects and advantages ofthe instant invention will become readily apparent to those skilled inthe art from the following detailed description of the preferredembodiments thereof taken in conjunction with the drawings in which:

FIG. 1 is a perspective view, with the back end removed and portionsbroken away, of a recuperated gas turbine engine according to theinstant invention;

FIG. 2 is a view from the back end of FIG. 1;

FIG. 3 is a schematic view showing the flow of air and gases through therecuperator of the instant invention;

FIG. 4 is a vertical sectional view taken through line 4--4 of FIG. 2;

FIG. 5 is a horizontal sectional view taken through line 5--5 of FIG. 2;

FIG. 6 is an enlarged view of the area identified by circle 6--6 in FIG.4;

FIG. 7 is an enlarged view of the area identified by circle 7--7 in FIG.5;

FIG. 8 is a fragmentary perspective view of the central shell of therecuperator according to the present invention;

FIG. 9 is a view similar to FIG. 8 showing the central shell of therecuperator with turbulators added;

FIG. 10 is a perspective view showing a turbulator according to thepresent invention;

FIG. 11 is a fragmentary sectional view through the central recuperatorshell shown in FIG. 9;

FIG. 12 is a top view showing the surface pattern of the turbulatorshown in FIG. 10;

FIG. 13 is a view similar to FIG. 12 showing an alternative surfacepattern for the turbulator;

FIG. 14 is a view similar to FIGS. 12 and 13 showing another alternativesurface pattern;

FIG. 15 is a perspective view showing a preparatory step in a method ofmaking the turbulator of FIG. 10.

FIG. 16 is a perspective view showing a method of forming the surfacepattern of FIG. 12;

FIG. 17 is a perspective view showing an alternative surface pattern;

FIG. 18 is a perspective view showing a further step in the method ofmaking the turbulator;

FIG. 19 is a top view of FIG. 18;

FIG. 20 is a bottom view of FIG. 18;

FIG. 21 is a sectional view taken through line 21--21 of FIG. 18;

FIG. 22 is a flow chart of a cogeneration system using the recuperatorof the instant invention;

FIG. 23 is a perspective view from the rear, similar to FIG. 2, showinga recuperated engine for use with the cogeneration system of FIG. 22;

FIG. 24 is a fragmentary vertical section of the engine of FIG. 23;

FIG. 25 is a flow chart of a second cogeneration system utilizing therecuperator of the present invention;

FIG. 26 is a front view of a recuperated engine for use with thecogeneration system of FIG. 25;

FIG. 27 is a rear view of the recuperated engine of FIG. 26;

FIG. 28 is a flow chart of an integrated air cycle-gas turbine engineusing the recuperator of the present invention; and

FIG. 29 is a perspective view showing the integrated air cycle-gasturbine engine of FIG. 28.

PREFERRED EMBODIMENT OF THE PRESENT INVENTION

Turning now to the drawings in which like reference characters indicatecorresponding elements throughout the several views, attention is firstdirected to FIGS. 1-5, which show a recuperated gas turbine engine 10according to the present invention.

The engine 10 includes a generally tubular casing 12, one end of whichcarries the collector 14 of a centrifugal compressor 16 having animpeller 18 which compresses incoming air and directs it generallyradially through a pipe diffuser 20. The air from the diffuser 20 entersa generally conical header 22 extending along substantially the entirelength of the top of the casing 12. From the header 22, the air enters arecuperator, or heat exchanger, 24 where it is preheated before beingexpelled into a conical bottom header 26 and through a connecting duct28 into a combustion chamber 30. In the combustion chamber 30, the airis ignited with fuel from an atomizer 32, producing extremely hot gaseswhich are then directed into the scroll 34 of a radial inlet turbine 36.The gases are expanded in the turbine 36 and discharged axially throughthe turbine nozzle 38 into a central chamber 40. From the centralchamber 40, the gases move back through the recuperator 24 to an axialexhaust 42.

Still referring to FIGS. 1-5, with additional reference to FIGS. 6-8,the recuperator 24 comprises three concentric cylindrical shells whichcompletely wrap around or encircle the hottest components of the engine10, including the combustor 30, turbine nozzle 38, and central chamber40. The outermost shell 44 includes a plurality of longitudinally spacedapart inlet openings 46 which open into the upper header 22 to receiverelatively low temperature air from the compressor 16. A plurality oflongitudinally spaced apart outlet openings 48 located diametricallyopposite the inlet openings 46 open into the bottom header 26. Theinnermost shell 50 includes a plurality of inlet openings 52 which arelocated at approximately the same radial position as the outlet openings48 of the outermost shell 44, and which open into central chamber 40 toreceive high temperature gases exhausted from the turbine 36. Aplurality of outlet openings 54 located diametrically opposite the inletopenings 48 and at approximately the same radial location as the inletopenings 46 of the outermost shell 44 open into exhaust duct 42.

The central shell 56, as best seen in FIGS. 6-8, is a corrugated tubewhich acts as a separator wall preventing mixing of the high pressureair discharged from the compressor with the low pressure gases exhaustedfrom the turbine, but allowing heat transfer therebetween. The spacesbetween each corrugation, or fold, 58 of the central shell 56 and theoutermost shell 44 define a plurality of annular flow chambers 60 forthe high pressure, relatively low temperature air, while thecorresponding spaces between the central shell 56 and the innermostshell 50 define a plurality of annular flow chambers 62 for the lowpressure, high temperature turbine exhaust gases. As is clear from FIG.3, the low temperature air from in the outer chambers 60 travels in thedirection opposite to the flow of high temperature gases in the innerchambers 62. Thus, the recuperator 24 is classified as a counterflowheat exchanger. In addition, since the thin corrugated wall of thecentral shell 56 is the only surface through which heat is conducted,the recuperator 24 is also classified as a primary surface heatexchanger. The counterflow, primary surface arrangement results inoptimal heat transfer

Because the gases exhausted from the turbine 36 are extremely hot(approximately 1,400° F.) relative to the air discharged from thecompressor 16 (approximately 350° F.), special provisions must be madeto minimize thermal stresses in the recuperator 24. Accordingly, amounting arrangement which allows the inner shell 50 of the recuperator24 to expand freely in response to temperature increases is shown inFIGS. 6 and 7. Specifically, the end of inner shell 50 on the exhaustside of the engine 10 includes a radially out-turned flange 64 which isloosely clamped between a terminal fold 58 of the central shell 56 andthe end wall 66 of the casing, as shown in FIG. 7. The flange 64 is freeto increase in length in response to increases in temperature. Inaddition, the opposite end of the inner shell is totally unrestrained,as shown in FIG. 6, to allow the shell to expand in an axial direction.Similarly, ample space is provided between the crests of each of thefolds 58 of the central shell 56 and the inner shell 50 to allow thefolds 58 to expand radially inwardly.

Outer shell 44, on the other hand, is subjected to much smallertemperature increases and does not expand significantly when the engine10 is in use. Accordingly, the opposite ends of the outer shell 44 maybe fixedly secured by, for instance, resistance welding to the enginecasing 12, as shown at 68. The opposite ends of the central shell 56 mayalso be welded to the outer shell, as shown at 70. Although the ends ofthe central shell 56 are constrained, the corrugations 58 are free torespond to thermal changes by compressing and expanding longitudinallyin much the same manner as the individual folds of a bellows. Sincethermal expansion in a transverse direction is already provided for bythe spacing between the crests of the corrugations 58 and the innershell 50, to such spacing is required between the opposite sides of thecorrugations and the outer shell 44.

Although the strength requirements of the recuperator 24 are minimal,the inner shell 50 is vulnerable to oxidation because of the extremelyhigh temperatures to which it is subjected. Accordingly, the inner shell50 must be formed of corrosion-resistant material, such as a high gradealloy. The central shell 56 and the outer shell 44 may be formed of lesscorrosion-resistant materials, such as lower grade alloys, since theyare less prone to oxidation, and since the minimal brazing required inthe mounting arrangement of FIGS. 6 and 7 eliminates the need for outershell 44, inner shell 50, and central shell 56 to be formed ofcompatible materials.

FIG. 10 shows a turbulator 72 suitable for inclusion between thecorrugations 58 of the central shell 56. The turbulator 72 comprises aring 74 having its inner circumference 76 crimped to form a wavysurface. A plurality of openings 78 extend through the surface to allowfluid to pass from one side of the ring 74 to the other. The ring 74 ispreferably not continuous, but includes a pair of slightly spaced apartends 80, 82 which allow for expansion and compression in acircumferential direction.

The size, shape, pattern, and number of openings 78 may be selectedaccording to the design requirements of the engine 10, and the amount ofturbulence required. FIGS. 9-12 show a pattern of circular openings 78which may be suitable for certain applications. FIG. 13 shows analternative pattern of transversely extending rectangular openings 78A,which may be suitable for other applications, while FIG. 14 shows stillanother pattern, comprising multiple rows of longitudinally extendingrectangular openings 78B, which may be suitable for yet otherapplications.

Each turbulator 72 is inserted into one of the annular chambers 60 or 62of the recuperator 24 such that the turbulator 72 is coaxial with thecentral shell 56, and the waves or undulations 84 formed by the crimpedinner edge 76 of the ring 74 are generally perpendicular to the folds ofthe shell 56, as shown in FIGS. 9 and 11. The alternating crests of thewaves 88 are essentially clamped between the folds 58, thus mechanicallyholding the turbulators 72 in place. Although FIGS. 9 and 11 show theturbulators 72 positioned in only the inner, high temperature chambers62 of the recuperator 24, it will be clear to the practitioner ofordinary skill in the art that they may be similarly positioned in theouter, lower temperature chambers 60 as well.

A simple, low cost method of forming the turbulators 72 of the presentinvention is illustrated in FIGS. 15-20. First, a metal having desiredproperties such as corrosion-resistance is rolled into sheet form, asshown in FIG. 15, and cut into rectangular strips 84 using appropriatecutting tools 86. The length L of each strip 84 is selected to equal thedesired outer circumference of the turbulator 72.

Next the sheet 84 is sheared between a punch 88 and a die block 90 toproduce a plurality of circular openings 78, as shown in FIG. 16, oropenings of other configurations, such as the rectangular openings 78Bshown in FIG. 17.

Finally, the sheet 84 is passed between a pair of specially configuredcrimping rollers 92, 94, as shown in FIGS. 18-21. The upper end 96 ofeach roller is circular, while the lower end 98 comprises a plurality ofrounded teeth 100. The rollers are arranged such that their longitudinalaxes are parallel, and the circular upper ends share a common tangent,while the rounded teeth 100 of the lower ends 98 mesh along curved linelocated below the point of tangency.

As the sheet 84 passes between the rollers 94, 96 the lower edge 102 ofthe sheet 84 is crimped between the meshing teeth 100 of the rollers.This crimping action effectively decreases the length 1 of the loveredge 102 of the sheet relative to the length L of the upper edge 104. Asthe difference between the length L of the upper edge 104 and the length1 of the lower edge 102 increases, the sheet 84 begins to curve about anaxis perpendicular to the axes of the rollers 92, 94, until eventuallythe sheet 84 forms a ring 24, as shown in FIG. 10. The upper edge 104 ofthe sheet is now the outer circumference of the ring 74, and the loweredge 102, is the inner circumference of the ring 74. Thus, the diameterof the rollers 92, 94 and the number of rotations necessary to form thering 74 can easily be calculated, using simple algebraic and geometricequations when the desired inner and outer diameters of the turbulatorring 74 are known.

Other methods of manufacturing the turbulator 72 may of course be used.However, the rolling technique disclosed herein is believed to be morecost effective than common massmanufacturing processes, such asstamping, for producing a limited number of annular turbulators.

Turning now to FIGS. 22-24, a cogeneration system 102 using therecuperated engine 10 of the present invention is shown. As describedearlier, the engine 10 comprises a compressor 16, which receivesatmospheric air from a collector or inlet filter 14, compresses it, andpasses it on to a combustion chamber or burner 30, where it is ignitedto produce high temperature gases. The high temperature gases are thenexpanded in the turbine 36, which converts the energy of the gases intouseful work. Interposed between the compressor 16 and the burner 30 isthe recuperator 24, the high temperature side 62 of which receives thegases exhausted from the turbine 36 for preheating the air in the lowtemperature side 60 as it passes from the compressor 16 to the burner.

In the embodiment of FIGS. 1-5, all of the waste heat from the turbine36 is directed into the high temperature side 62 of the recuperator 24,and is then dumped into the atmosphere via the exhaust duct 42. Such asystem is wasteful from an energy standpoint, and undesirable from anenvironmental standpoint since much of the gas exhausted my be noxious.In the cogeneration system 102 of this embodiment, such problems areeliminated by coupling the output end of the exhaust duct 42 to a boiler104 or other energy recovery device, where the exhaust heat is used toproduce steam heat or similar useful energy. Furthermore, a valve 106 isplaced in the end wall 66 of the engine casing 12 to selectively allow acontrolled volume of the turbine exhaust gases in central chamber 40 toenter a duct 108 which bypasses the recuperator 24 and merges with theturbine exhaust duct 42 to deliver the gases directly to the boiler 104.

The action of the valve 106 is governed by a control circuit 109 whichreceives input from a thermocouple 110 located in the boiler 104 toensure that the temperature of the gases entering the boiler 104 remainssubstantially constant. This is achieved by regulating the volume of gaspassing through the recuperator 24 relative to the volume of gasespassing through the bypass duct 108. For example, if the thermocouple110 detects that the temperature of gases entering the boiler 104 hasfallen below the desired level, the valve 106 will move into an openposition, allowing some or all of the gas to bypass the recuperator 24.The temperature of the gas which bypasses the recuperator will be nearlythe same as the outlet temperature of the turbine 36, and thus will acteffectively to raise the temperature in the boiler 104. On the otherhand, if the thermocouple 110 senses that the inlet temperature of theboiler 104 has risen above the desired level, the valve 106 will moveback towards its closed position, so that a larger volume of gas passesthrough the recuperator 24. The gas in the recuperator 24 loses a greatdeal of heat to the air exhausted from the compressor 16, thus bringingthe inlet temperature of the boiler 104 back down to its desired levelin a relatively short period of time.

In the cogeneration system 112 illustrated in FIGS. 25-27, the wasteheat from the turbine 36 is exhausted into a boiler 104 as in theprevious system 102, with a bypass conduit 108, valve 106, andthermocouple 110 being provided to maintain the boiler inlet temperatureat a constant level. However, in this system, still more work is derivedfrom the engine 10 by adding additional stages of compression, heating,and expansion.

Specifically, a second compressor 114 is added downstream of the firstcompressor 16, and an air-to-water heat exchanger, or intercooler, 118is interposed between the two compressors 16, 14. The intercooler 118utilizes part of the heat of the air exhausted from the first compressor16 to raise the temperature of cold water entering through an inlet duct120. The warmed water is then discharged through an outlet duct 122which delivers the water to the boiler 104. A second duct 124 may alsobe provided for delivering the water to an alternative output device,such as a faucet 126, with a valve 128 being provided for selectivelycontrolling the volume of water delivered to the boiler relative to thevolume delivered to the alternative output device 126.

The cogeneration system 112 also comprises a second turbine 130 fordriving the second compressor 114, and a second combustion chamber 132interposed between the turbines 36, 130, for reheating the gasesexhausted from the second turbine 130 before their entry into the firstturbine 36. The additional stages of compression, expansion andreheating serve to increase the temperature and pressure ratios of theengine 10, and thus increase the net energy output of the system 112.

Finally, FIGS. 28 and 29 illustrate a system 134 in which therecuperated engine 10 of the present invention is integrated with an airconditioning or cooling cycle. In this system 134, an additional turbine136, an air-to-water heat exchanger 138, and an air-to-air heatexchanger 140 are added upstream of the engine 10. Incoming air atatmospheric temperature is expanded and cooled in the additional turbine136 and then passes through the air-to-water heat exchanges 138, whereit is used to cool warm water entering through an inlet duct 142 to asuitable drinking temperature. The cooled water is then dischargedthrough an outlet duct 144. The air, which is still cooler thanatmospheric temperature despite having been warmed in the air-to-waterheat exchanger, pre-cools the incoming atmospheric temperature air.

The output shaft of the additional turbine 136 is coupled to anadditional compressor 146 downstream of the original compressor 16 ofthe engine 10. As a result, the pressure of the compressed air enteringthe combustion chamber 30 is lower than in the simplified version of theengine 10 illustrated in FIGS. 1-5, and the net pressure ratio andperformance of the engine 10 are increased correspondingly. Other thanthis, the structure and function of the remaining components of theengine 10 are identical to those of their counterparts in the firstembodiment.

One potential application for the integrated system 134 illustrated inFIGS. 28 is in military operations in the desert, where there is a needfor low cost, lightweight power generation devices and cool drinkingwater for military personnel.

Various changes and modifications to the embodiment herein chosen forpurposes of illustration will readily occur to those skilled in the art.To the extent that such modifications and variations do not depart fromthe spirit of the invention, they are intended to be included within thescope thereof which is assessed only by a fair interpretation of thefollowing claims.

Having fully described the invention in such clear and concise terms asto enable those skilled in the art to understand and practice the same,the invention claimed is:
 1. An integrated air cycle-gas turbine enginecomprising:a) air entry means for receiving air at atmosphericconditions; b) a first turbine downstream of said air entry means forexpanding and cooling said air; c) an air-to-water heat exchangerdownstream of said first turbine, said air-to-water heat exchangerincludingi) air inlet means for admitting cooled expanded air from saidfirst turbine; ii) air outlet means for expelling said expanded air;iii) water inlet means for admitting warm water; iv) water outlet meansfor discharging said water; and v) separator means for separating saidexpanded air from said water and conducting heat therebetween; d) anair-to-air heat exchanger downstream of said air-to-water heatexchanger, said air-to-air heat exchanger includingi) first inlet meansfor receiving expanded air from said air outlet means of saidair-to-water heat exchanger; ii) first outlet means for discharging saidexpanded air; iii) second inlet means communicating with said air entrymeans for receiving atmospheric air; iv) second outlet means fordischarging said atmospheric air into said first turbine; and v)separator means for separating said expanded air from said atmosphericair and conducting heat therebetween; e) a combustion chamber havingmeans supplying fuel thereto; f) a first compressor, driven by saidfirst turbine, for supplying compressed air to said combustion chamber;g) a second compressor, downstream of said air-to-air heat exchanger andupstream of said first compressor, for receiving expanded air from saidfirst outlet means and pre-compressing said air prior to entry into saidfirst compressor; h) a second turbine, downstream of said combustionchamber, for extracting energy produced in said combustion chamber anddriving said second compressor; and i) a recuperator includingi) firstinlet means for admitting compressed air from said first compressor; ii)first outlet means for expelling said compressed air; iii) second inletmeans for admitting high temperature exhaust from said second turbine;iv) second outlet means for expelling said exhaust; and v) separatormeans for separating said compressed air from said turbine exhaust andfor conducting heat therebetween.
 2. An integrated air cycle-gas turbineengine according to claim 1, wherein said recuperator is a primarysurface counterflow heat exchanger encircling said second turbine andsaid combustion chamber.